1. Field of the Invention
The present invention relates to an optical communication apparatus which uses an optical signal as a signal transmitting medium, and more particularly, to an apparatus which receives an optical signal transmitted from a transmitter which emits an optical signal.
2. Description of the Prior Art
An optical communication apparatus is conventionally known which, using light receiving elements such as a photodiode as a light receiving element, receives an optical signal emitted from a signal transmitting apparatus by means of the above-described light receiving element, so that information can be transmitted from distant places.
In such an apparatus, the photodiodes generates photoelectric current which corresponds not only to the intensity of light emitted from the signal transmitting apparatus but also to the intensity of peripheral light such as shot noise and pulse light generated from fluorescent lamps. This may cause the optical signal receiving apparatus to be incorrectly operated, with the result that information transmitted from a transmitter may be incorrectly received by the light receiving apparatus.
Furthermore, in such conventional device, signal/noise ratio is deteriorated when it is used outdoors because the intensity of peripheral light such as sun-light is much higher than that of transmitted optical signal.
It is known that in some of such receiving apparatuses, a photoelectric element is used as the optical signal receiving element and a resistor is connected in series to the photoelectric element.
The above-described structure, when used outdoors, is disadvantageous in that photosensitivity is deteriorated because it is difficult for the photoelectric current corresponding to the signal light to flow in a circuit. This is caused by the fact that electric potential increases at connection point of the photoelectric element and the resistor, to be approached to the power supply voltage owing to the increase of the photoelectric current caused by increase of the intensity of surrounding light.
Therefore, conventional optical communication apparatuses have a disadvantage in which correct signal communication can be achieved in relatively short distance range when the intensity of light on the light receiving element is relatively high, and in which it can be achieved in relatively long distance range when the intensity is relatively low.